Torque converter lockup control

Abstract

A control for providing a smooth, high quality torque converter lockup event in an automated mechanical transmission system (10) including a fuel-controlled engine (12) and a mechanical transmission (14) drivingly coupled by a torque converter and torque converter lockup clutch assembly (16). To achieve smooth torque converter lockup, engine torque is smoothly ramped down to a relatively low value and maintained at that value until the torque converter lockup clutch is effectively engaged.

We claim: 
     
       1. A method for controlling an automated mechanical transmission system comprising a fuel-controlled engine, an engine controller for controlling fueling of the engine, a multiple-speed mechanical transmission, and a torque converter and torque converter lockup clutch mechanism for drivingly coupling the transmission to the engine, said method comprising the steps of: (a) sensing values of parameters indicative of system operating conditions;   (b) determining a response time (Tres) for the lockup clutch to engage;   (c) determining a desired engine torque value (Tdwe) for engagement of the lockup clutch;   (d) determining a desirable rate for decreasing engine torque to said desired engine torque value (RATE);   (e) upon sensing a requirement for engaging the torque converter lockup clutch, causing engine torque to decrease at said desirable rate to said desired engine torque value and initiating engagement of said lockup clutch to engage only when or after said engine torque is equal to said desired engine torque value.   
     
     
       2. The method of claim 1 wherein said desired engine torque value is no greater than 10% of full engine torque. 
     
     
       3. The method of claim 1 further comprising the steps of: (f) determining a desirable rate for increasing engine torque after engagement of the lockup clutch; and   (g) after engagement of said lockup clutch, causing engine torque to increase from said desirable engine torque to a torque value requested by the operator at said desirable rate for increasing engine torque.   
     
     
       4. The method of claim 1 wherein said desirable rate to decrease engine torque is about 1% of full engine torque every 10 milliseconds. 
     
     
       5. The method of claim 1 wherein said desired engine torque value is no greater than 20% of full engine torque. 
     
     
       6. The method of claim 5 wherein said desirable rate to decrease engine torque is about 1% of full engine torque every 10 milliseconds. 
     
     
       7. The method of claim 1 wherein the requirement for engaging said lockup clutch is determined as a function of engine speed. 
     
     
       8. The method of claim 7 wherein the requirement for engaging said lockup clutch is also determined as a function of operator-set throttle position. 
     
     
       9. The method of claim 1 wherein step (e) comprises: (i) sensing current engine torque at initiation of a torque converter lockup clutch lockup event;   (ii) determining the time (Treq) required to decrease engine torque to said desired engine torque value; and (a) if the time required to decrease engine torque to said desired engine torque value exceeds said response time (Treq>Tres), then initiating engagement of the lockup clutch only after a time period equal to the time required minus the response time (Treq-Tres) after beginning to decrease engine torque.     
     
     
       10. The method of claim 9 further comprising step (ii)(b), if the response time exceeds the time required (Tres>Treq), then immediately initiating engagement of the lockup clutch. 
     
     
       11. A system for controlling an automated mechanical transmission system comprising a fuel-controlled engine, an engine controller for controlling fueling of the engine, a multiple-speed mechanical transmission, and a torque converter and torque converter lockup clutch mechanism for drivingly coupling the transmission to the engine, said system comprising: (a) means for sensing values of parameters indicative of system operating conditions;   (b) means for determining a response time (Tres) for the lockup clutch to engage;   (c) means for determining a desired engine torque value (Tdwe) for engagement of the lockup clutch;   (d) means for determining a desirable rate for decreasing engine torque to said desired engine torque value (RATE);   (e) means effective, upon sensing a requirement for engaging the torque converter lockup clutch, to cause engine torque to decrease at said desirable rate to said desired engine torque value and initiate engagement of said lockup clutch to engage only when or after said engine torque is equal to said desired engine torque value.   
     
     
       12. The system of claim 11 wherein said desired engine torque value is no greater than 10% of full engine torque. 
     
     
       13. The system of claim 11 further comprising: (f) means for determining a desirable rate for increasing engine torque after engagement of the lockup clutch; and   (g) means effective, after engagement of said lockup clutch, to cause engine torque to increase from said desirable engine torque to a torque value requested by the operator at said desirable rate for increasing engine torque.   
     
     
       14. The system of claim 11 wherein said desirable rate to decrease engine torque is about 1% of full engine torque every 10 milliseconds. 
     
     
       15. The system of claim 11 wherein said desired engine torque value is no greater than 20% of full engine torque. 
     
     
       16. The system of claim 15 wherein said desirable rate to decrease engine torque is about 1% of full engine torque every 10 milliseconds.